Seeburg 222 amp problem

Working on a Seeburg model 222 . Amp .. SHFA2 .

I have redone 4 of these with no problem . This one however is not cooperating . I have done all the usual , capacitors , resistors , cleaning .....
It works , plenty of volume and bass . However it sounds crappy . I will try to describe this 2 ways .
At any volume it sounds distorted like the input is being over driven . Or it sounds like the output tubes bias is off causing crusty sound .

I have subbed in all different tubes . I have tried different cartridges & new needles .Tried to put resistance between the cartrige and amp . I unhooked the input plug from the amp and hooked in an ipod and still get the distortion with the ipod at any level . I even tapped in ahead of the transistor out stage . Also tried a variac to lower the voltage .

Any ideas ? Anyone have a tube voltage chart for this ?

Some things to do:

1) Are the speakers at fault? Try subs.

2)Get a schematic: http://arcarc.xmission.com/PDF_Jukebox/Seeburg/ Voltages are there.

3) Since distortion seems to be constant at any level, this throws suspicion to the preamp-voltage amps and tone stages. If you have an external test amp connect it to the high side of the volume control. The schematic will show that point. A tube type test amp is preferable due to the high B+ in these old amps.

Is distortion on both channels?

A scope and signal generator would speed things up...but only a bit. If you are sure that distortion does not increase with volume control setting and the speakers are OK, I would suspect the preamp stages.

Rob/NYC

Thanks Ron
Speakers are good and both channels are affected. Thanks for the schematic i will report back.

Ken,
That was Rob, not Ron who posted the above good advice--
I think I might look at the transistors, and / or the AVC circuit for a problem of that nature--
Ron Rich

Thanks Ron . My mind drifts & skips lately ( probably why the amp dont work ) Today i turned it back on using the records . It sounded much better but as time went on ( aprox 20 minutes ) the sound got ugly . I hooked an external amplifier to the volume control and got the same bad sound from that amp .
Next thing i found the input pins on the 2 .. 12AX7 tubes up next to the output tubes trying to eliminate the rest of the amp , hooked an ipod there and got even worse sound .
At this time i pulled out all 4 output tubes ( with a towel ipod same place & going ) and installed 2 new in box tubes into the right side and then switched them to the left side . The sound did not improve on either side . I still need to print the chart provided and check voltages .
Now i wonder if both sections of this amp have a problem . But on both channels .. wierd .

Given that it affect both channels, I think your hunch to check voltages is a good place to look.

Start with the power supply as this affect both channels and look for trending voltages as the machine warms up. This is typical of leaky caps, but gassy tubes can cause a heavy drain on the P.S. too.

Check to see if the volume control has been messed with. I once had VL amp where some 'hole had wired the arm of the volume pot to the -preamp- side. Needless to say, it didn't sound very good at low levels.

Rob

Rob,
Come on now man--be consistent ! "--some 'hole--" ? Don't you mean "gepetto" ??
Ron Rich

This amp was never messed with before , in fact it had all of its original seeburg tubes . Capacitors have been replaced & tubes changed and swapped . Resistors checked ( like in the other 4 i did )

This will be a long road i think I have evil thoughts of having a big fire and let the neighbors cook dinner over it

Ken, the key here is to find what affect both channels. The main point is the power supply.

Attach your meter to various points in the filter and bias supplies, make notes with the amp "cold" where you say it sounds better. Then recheck those voltages as things deteriorate.

There is a remote possibility that the amp is oscillating at a high frequency. One way to test for this is to use a large value capacitor approx 1 mfd and use it to ground out various tube inputs.

It is also possible that -both- output trans are bad. This unfortunately is not that unusual as the 6973's are prone to shorting and with no cathode resistor to limit the current the tran takes the brunt of the damage if not caught in time. The good news is that -if- the signal from the volume control is distorted too, the output trans are not likely the culprit.

Remove both 6BJ6 AGC tubes and also test the two AGC diodes (CR101 & 102).

Fifteen years ago+ I would have made you an offer for that amp as-is. I'm damn cheap and buying people's "impossibles" is how I built my supply of spares.

Rob/NYC

Rob

Ken,
What makes you think it still had all of "it's original tubes" ?
Unless "code date" stamped, with either a yellow, or orange rubber "S" stamp, I kinda doubt it.
Seeburg brand/marked replacement tubes were available to at least 1979 from Seeburg. ( I still have a few NOS in stock !)
Ron Rich

What makes you think it still had all of "it's original tubes" ? .............

Because they all say seeburg on them and they are all the same as for dirt on them . I had no idea they used seeburg brand tubes as replacements . The whole entire machine looked untouched too .

I got bussy at work so i have not been back into this ...yet . Thanks for the tips so far .

Got this fixed . I gave up and took it to a shop here that has all the scopes & equipment to track down such things . 2 things were wrong . First the schematic had a wrong value capacitor in the bias circuit marked .2mfd that should have been 100mfd and i missed 2 .001 caps buried deep under stuff .

Sounds fine now .

Ken,
Which cap is mis-marked, on which version of the schematic ?
Yea--I also missed one of those "buried" .001's on the first one I rebuilt--many moons ago--but I still remember it !

Ron Rich

What schematic are you looking T? the one I linked has the three L-V filter caps at;

C167: 20@75vdc
C168: 65@40vdc
C170 " "

Most likely someone messed up the 20mfd but knowledge of electronics would have prevented that.

I think I've had enough of 'troubleshooting by proxy"..


"Bye for now,

Rob

It is the schematic from the link above . C 155 is listed as .20mfd 75v lytic .

When i recapped the amp first it had all of its original caps in it . C 155 was one of those white ceramic marked 100mfd 75v so thats what i used . After i saw the schematic i changed it to a .2 in an effort to fix the thing . The other tech saw that as wrong and put a 100 back in .

Schematics BLAAA